Strain amplification structure and synthetic jet actuator

ABSTRACT

A strain amplification structure has a frame with a hexagonal structure incorporating a plurality of rigid beams that are connected to opposing end beams by a plurality of flexible joints. A piezoceramic actuator assembly is connected to the opposing end beams having a collar including an opening. A shaft providing an output is connected to the plurality of rigid beams with flexible joints and passes through the opening in the collar for non-interfering motion orthogonal to the actuator assembly.

REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/524,878 filed on Jun. 15, 2012 entitled STRAIN AMPLIFICATIONSTRUCTURE AND SYNTHETIC JET ACTUATOR and having a common assignee withthe present application, the disclosure of which is incorporated hereinby reference.

BACKGROUND INFORMATION

1. Field

Embodiments of the disclosure relate generally to the field of syntheticjet actuators and more particularly to a mechanical amplifier actuationsystem with minimized translating mass for coupling of mechanical andacoustical amplification for creating a synthetic jet.

2. Background

Synthetic jets are being employed for control of flow on variousaerodynamic surfaces, Boundary layer control for drag reduction toincrease fuel efficiency and for aerodynamic controls on flight vehiclesas well as turbulence reduction for improved aero-optical performance ofelectro-optical turrets have been demonstrated with synthetic jets.

The small size and high frequency operation of synthetic jets allows useof piezoelectric actuators for creation of pumping devices to create thejet. However, the small physical extension and contraction ofpiezoelectric devices requires amplification for enhanced operation.Various amplification systems have been employed for piezoelectricactuators. A basic flexible rombus structure such as flexure 2 shown inFIG. 1 has been employed to create amplified motion of a piezoelectricstack 3. Lateral motion of the piezoelectric stack as represented byarrows 4 results in longitudinal extension of the flexure as shown byarrow 5 with an amplification created by the flexure between a firstvertex 6 and a second vertex 7 in the flexure. For driving a piston in asynthetic jet device, the flexure must be constrained at one vertex withmotion output at the second vertex. As a result, the entire flexureincluding the contained piezoelectric stack with all associatedelectrical connections translates during activation.

It is therefore desirable to provide an amplification device forpiezoelectric actuation which minimizes translational mass and toprovide a synthetic jet with a maximized amplification transferfunction.

SUMMARY

Embodiments disclosed herein provide a strain amplification structurehaving a frame with a hexagonal structure incorporating a plurality ofrigid beams that are connected to opposing end beams by a plurality offlexible joints. A piezoceramic actuator assembly is connected to theopposing end beams having a collar including an opening. A shaftproviding an output is connected to the plurality of rigid beams withflexible joints and passes through the opening in the collar fornon-interfering motion orthogonal to the actuator assembly.

In an example application a synthetic jet actuation structure is createdwith an amplification structure frame having laterally spaced flexingend beams, a first pair of opposing actuation beams angularly extendingfrom the end beams and a second pair of opposing actuation beamsextending angularly from the end beams, parallel to and longitudinallyspaced from the first pair of opposing actuation beams. A center shaftis suspended by the first pair of opposing actuation beams and thesecond pair actuation beams. A piezoceramic actuation assembly extendsbetween the end beams in a non-interfering relationship with the centershaft. The piezoceramic actuation assembly has a first condition placingthe end beams in a first relative lateral position with the first andsecond pair of actuation beams extending at a first angle from the endbeams to place the shaft in a first longitudinal position and a secondcondition placing the end beams in a second relative lateral positionwith the first and second pair of actuation beams extending at a secondangle from the end beams to place the shaft in a second longitudinalposition. A piston is connected to the center shaft and a housing havinga cavity receives the piston. An orifice provides an output from thecavity to create a synthetic jet upon reciprocation of the piezoceramicactuation assembly between the first and second condition.

The embodiments disclosed provide a method fur creating a synthetic jetby interconnecting laterally spaced flexing end beams with a first pairof opposing actuation beams angularly extending from the end beams and asecond pair of opposing actuation beams extending angularly from the endbeams, parallel to and longitudinally spaced from the first pair ofopposing actuation beams. A center shaft with a piston is suspended fromthe first pair of opposing actuation beams and the second pair actuationbeams. A piezoceramic actuation assembly connected between the end beamsand intermediate the first and second pair of actuation beams isreciprocated on a non-interfering basis with the center shaft. Thepiston is received in a housing cavity having an orifice to create thesynthetic jet.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments further details of which canbe seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a prior art piezoelectricamplification structure;

FIG. 2 is pictorial view of an embodiment of a mechanical amplificationsystem for piezoceramic stacks for a synthetic jet;

FIG. 3 is aside view of the embodiment of FIG. 2;

FIG. 4 is a schematic representation of an unextended position of theamplification system and an extended position of the amplificationsystem;

FIG. 5 is a pictorial view of an exemplary synthetic jet employing theamplification system embodiment of FIG. 2;

FIG. 6 is an exploded view of the synthetic jet of FIG. 5;

FIG. 7 is a graph of the amplification transfer function of theexemplary synthetic jet;

FIG. 8 is a side section view of two opposed mechanical amplificationsystem of the described embodiment driving a single piston for asynthetic jet; and,

FIG. 9 is a flow chart of a method for creation of a synthetic jetemploying coupled amplification of a piezoceramic stack.

DETAILED DESCRIPTION

Embodiments disclosed herein provide a strain amplification structure.The structure includes a rhombus-like hexagonal frame or flexure. Theframe incorporates a plurality of rigid beams connected together byflexible joints. A pair of piezoceramic stack actuators such as LeadZirconate Titanate (PZT), internal to the frame, act against the framecausing the frame to change from an undeflected state to a deflectedstate. A shaft connecting an attachment point to an output extendsthrough an aperture in a base that is common to the pair of PZT stackactuators. The shaft can be used to drive a variety of devices such as apump for a synthetic jet application.

Referring to the drawings, FIGS. 2 and 3 show an embodiment of anamplification structure frame 10. Laterally spaced flexing end beams 12a and 12 b support the structure from attachment brackets 14 a and 14 bwhich may be attached to a rigid support for the entire amplificationstructure frame in applications such as a synthetic jet as will bedescribed in greater detail subsequently. A first pair of opposingactuation beams 16 a and 16 b extend angularly from the end beams 12 aand 12 b, respectively, to suspend a center shaft 18. A second pair ofactuation beams 20 a and 20 b, which are spaced longitudinally from thefirst actuation beam pair 16 a, 16 b, extend angularly from the endbeams 12 a and 12 b to the center shaft 18. Actuation beams 20 a and 20b are parallel to actuation beams 16 a and 16 b, extending from the endbeams 12 a and 12 b at the same relative extension angle 22 (best seenin FIG. 3). The actuation beams are interconnected to the end beams andcenter shaft with flexible joints 24. For the embodiment shown, thejoints 24 are flexible webs machined or etched between the end beams andactuation beams and the center shaft and actuation beams. In alternativeembodiments, pinned connections may be employed. The components of theamplification structure frame 10 may be fabricated from aluminum (anexample embodiment employs 2024 aluminum), titanium, beryllium orberyllium alloys such as beryllium copper, steel or carbon fiberreinforced plastics.

A piezoceramic actuation assembly 26 extends between the end beams 12 aand 12 b centered intermediate the first pair of actuation beams 16 a,16 b and second pair of actuation beams 20 a, 20 b. Activation ofpiezoelectric elements in the actuation assembly 26 provides lateralextension or contraction of the assembly which, in turn increases ordecreases the lateral distance 28 between the end beams. An increase inthe lateral distance of the end beams results in a reduction in theextension angle 22 of the actuation beam pairs while a decrease in thelateral distance results in an increase in the extension angle. Thevarying extension angle of the actuation beam pairs creates longitudinalmotion of the center shaft 18 along axis 30 with an amplification of therelative distance based on the variation of the extension angle 22.

The piezoceramic actuation assembly 26 operates orthogonally to thecenter shaft 18 on a non-interference basis. For the embodiment shown inFIGS. 2 and 3, this is accomplished with a collar 32 having an aperture34 through which the center shaft 18 extends. Two piezoceramic stacks 36a and 36 b extend oppositely from the collar 32 to the end beams 12 aand 12 b. Collar 32 in the embodiment shown in the drawings surroundsthe center shaft 18 with interlocking elements 33 a and 33 b. Inalternative embodiments, a collar in the form of a U or semi-cylindricalelement which partially surrounds the shaft may be employed. The collarmay additionally provide a clearance for the shaft in aperture 34, asfor the embodiment shown, or closely receive the shaft to act as a guideelement to limit shaft lateral deflection. in other alternativeembodiments, the piezoceramic actuation assembly may employ a singlepiezoceramic stack which extends from the end beams through a slot inthe center shaft. In any of the embodiments, the attachment brackets maybe rigidly mounted to a structure and the piezoceramic actuationassembly is maintained in a stationary position while the center shaftis translated longitudinally. This structure significantly reduces themoving mass allowing a higher translation frequency for the shaft 18 tobe created by the amplification structure frame 10.

As shown in FIG. 4, the unactuated amplification structure frame 10 awith piezoceramic stacks 36 a and 36 b in a relaxed or contracted stateplaces the end beams 12 a, 2 b in closest proximity with the actuationbeam pairs 16 a, 16 b and 20 a, 20 b at a maximum extension ante. Centershaft 18 is placed by the actuation beams at an initial longitudinal endpoint designated Y=0. The actuated amplification structure frame 10 bwith piezoceramic stacks 36 a and 36 b in an activated or extended stateas represented by arrows 38 urges the end beams laterally outward adistance ΔX which reduces the extension angle of the actuation beampairs approaching perpendicularity to the end beams resulting in alongitudinal motion of the center shaft 18 of ΔY. The center shafttranslates through the collar 32 allowing the piezoceramic actuationassembly to remain longitudinally static.

As shown in FIGS. 2 and 3, a piston 40 may be attached to the centershaft 18 for use in a synthetic jet generator. FIGS. 5 and 6 show anexemplary implementation for a synthetic jet having a housing 42 with acavity receiving the piston 40 and an outlet orifice 44. The housing 42includes a support ring 46 which engages the attachment brackets 14 aand 14 b to support the amplification structure frame 10. A centeringbearing 38 received in a sleeve in a superstructure (not shown) attachedto the housing 42 may be employed on the center shaft 18 to maintainaxial alignment during longitudinal reciprocation of the shaft oralternatively to provide a second motion output for the amplificationstructure frame. Sizing of the cavity 46 into which the piston isreceived including relative area between the piston and outlet orificecreates acoustic modes within the cavity which further amplify themechanical actuation provided by the amplification structure frame 10.Through coupling of the acoustic mode of the cavity, piston and outletorifice the synthetic jet actuator may be driven at either themechanical or acoustic resonance of the device. A measured transferfunction of the device shown in FIGS. 5 and 6 between voltage into thepiezoceramic actuation assembly 26 and the acceleration of the piston 40is shown in FIG. 7. In this example, the total displacementamplification of the piston at the measured peak 50 at around 1200 Hz isa factor of 10 over the motion of the piezoceramic stack alone. A lowerfrequency peak 52 is associated with uncoupled acoustic resonance whilethe higher frequency peak 50 is associated with uncoupled structuralresonance. In a coupled device, both structural and acoustic effects areinvolved in both resonances, but the lower frequency peak gives moremomentum in the example embodiment. The ability of the improvedsynthetic jet to tailor the displacement amplification of thepiezoceramic stacks while minimizing the mass that is subject tomechanical amplification (with the actuation assembly 26 held stationaryand translation of the center shaft only) allows a device that impartsgreater forces resulting in higher velocities of air through theorifice. For the example embodiment depicted by the data in FIG. 7, withan initial extension angle 22 for the actuation beam pairs of 8°mechanical amplification was factor of ˜3 and an area ratio of piston 40to outlet orifice 44 of approximately 100 produced resonantamplification of approximately 5. With initial extension angle 22 in arange of about 5° to 15° mechanical amplification of at least a factorof 5 is anticipated with varied area ratio from about 100 to 50.

The stationary positioning of the actuation assembly 26 for theembodiment shown in FIGS. 5 and 6 enhances the ability to employ twoopposed amplification frames 10 and 10′ to drive a single piston 40 asshown in FIG. 8 with actuation of the piezoelectric actuation assemblies26 and 26′ out of phase.

The embodiments described herein provide a method for amplifying themechanical actuation of a piezoceramic actuator assembly for use in asynthetic jet or other applications as shown in FIG. 9 Laterally spacedflexing end beams are interconnected with a first pair of opposingactuation beams angularly extending from the end beams, step 902, and asecond pair of opposing actuation beams extending angularly from the endbeams, parallel to and longitudinally spaced from the first pair ofopposing actuation beams, step 904. A center shaft with a piston issuspended from the first pair of opposing actuation beams and the secondpair actuation beams, step 906. A piezoceramic actuation assembly isconnected between the end beams and intermediate the first and secondpair of actuation beams, step 908. The piezoceramic actuation assemblyis reciprocated on a non-interfering basis with the center shaft, step910. Achieving the non-interfering condition between the actuationassembly and the center shaft may be accommodated by inserting thecenter shaft through a collar interconnecting two piezoceramic stacks inthe piezoceramic actuation assembly. The piston is connected to thecenter shaft and received in a housing cavity having an orifice tocreate the synthetic jet, step 912. The reciprocation of thepiezoceramic actuation assembly may occur at a first frequency toprovide a coupled mechanical resonance of the acoustic cavity forincreased amplification. The reduced reciprocating mass also allows theoperation at a second frequency for coupled resonance of the piston forincreased amplification.

Operation with a second actuation frame as shown in FIG. 8 isaccomplished by interconnecting a second pair of laterally spacedflexing end beams with a third pair of opposing actuation beamsextending at an inverse angle from the pair of end beams, step 914, anda fourth pair of opposing actuation beams extending at an inverse anglefrom the second pair of end beams, parallel to and longitudinally spacedfrom the third pair of opposing actuation beams, step 916. The centershaft with the piston is then also suspended from the third pair ofopposing actuation beams and the fourth pair actuation beams, step 918.A second piezoceramic actuation assembly is connected between the secondpair of end beams and intermediate the third and fourth pair ofactuation beams, step 920 and reciprocated on a non-interfering basiswith the center shaft out of phase with the first piezoceramic actuationassembly, step 922.

Having now described various embodiments of the disclosure in detail asrequired by the patent statutes, those skilled in the art will recognizemodifications and substitutions to the specific embodiments disclosedherein. Such modifications are within the scope and intent of thepresent disclosure as defined in the following claims.

What is claimed is:
 1. A strain amplification structure comprising: aframe having a hexagonal structure incorporating a plurality of rigidbeams that are connected to opposing end beams by a plurality offlexible joints; a piezoceramic actuator assembly connected to theopposing end beams; a collar in the piezoceramic actuator assembly, saidcollar including an opening; and a shaft providing an output andconnected to the plurality of rigid beams with flexible joints, saidshaft passing through said opening.
 2. The strain amplificationstructure as defined in claim 1 wherein the plurality of rigid beamscomprises: a first pair of actuation beams extending angularly from theend beams; a second pair of actuation beams extending angularly from theend beams longitudinally separated from the first pair of actuationbeams and parallel thereto, said piezoceramic actuators intermediate thefirst pair of actuation beams and the second pair of actuation beams. 3.The strain amplification structure as defined in claim 2 wherein thepiezoceramic actuator assembly comprises a pair of piezoceramic stackseach connected at an inner end to the collar and at an opposite end to arespective one of the end beams.
 4. The strain amplification structureas defined in claim 3 wherein a first condition of the piezoceramicstacks places the end beams in a first relative lateral position withthe first and second pair of actuation beams extending at a first anglefrom the end beams to place the shaft in a first longitudinal positionand wherein a second condition of the piezoceramic stacks places the endbeams in a second relative lateral position with the first and secondpair of actuation beams extending at a second angle from the end beamsto place the shaft in a second longitudinal position, a distance betweensaid first and second longitudinal positions comprising an amplificationof a second distance between the first and second lateral positions. 5.The strain amplification structure as defined in claim 4 furthercomprising: attachment brackets supporting the end beams for resilientlateral movement a housing from which the attachment brackets arerigidly supported; a piston attached to the shaft and received in acavity in the housing, said cavity having an orifice, wherebyoscillation of the piezoceramic stacks between the first and secondconditions creates a synthetic jet.
 6. The strain amplificationstructure as defined in claim 1 wherein the flexible joints are flexiblewebs machined or etched between the end beams and actuation beams andthe center shaft and actuation beams.
 7. The strain amplificationstructure as defined in claim 1 wherein the amplification structureframe is fabricated from a material selected from the set of aluminum,beryllium, beryllium alloys, titanium, steel and carbon fiber reinforcedplastic.
 8. The strain amplification structure as defined in claim 1wherein the piezoceramic actuator is operable to reciprocate at a firstfrequency providing mechanical resonance of the shaft for increasedamplification.
 9. The strain amplification structure as defined in claim5 wherein the piezoceramic actuator is operable to reciprocate at asecond frequency providing acoustic resonance of the piston, cavity andorifice.
 10. The strain amplification structure as defined in claim 5wherein the piezoceramic actuator reciprocation occurs at a frequency tocouple a mechanical resonance of the shaft and acoustic resonance of thepiston, cavity and orifice for increased amplification.
 11. A method forproducing a synthetic jet comprising: interconnecting a pair oflaterally spaced flexing end beams with a first pair of opposingactuation beams extending at an angle from the pair of end beams and asecond pair of opposing actuation beams extending at an angle from thepair of end beams, parallel to and longitudinally spaced from first pairof opposing actuation beams; suspending a center shaft with a pistonfrom the first pair of opposing actuation beams and the second pairactuation beams; reciprocating a first piezoceramic actuation assemblyconnected between the pair of end beams and intermediate the first andsecond pair of actuation beams on a non-interfering basis with thecenter shaft; receiving the piston in a housing cavity having anorifice.
 12. The method as defined in claim 11 wherein reciprocation ofthe piezoceramic actuation assembly occurs at a first frequency toprovide a mechanical resonance of the shaft for increased amplification.13. The method as defined in claim 11 wherein reciprocation of thepiezoceramic actuation assembly occurs at a second frequency foracoustic resonance of the piston, cavity and orifice.
 14. The method asdefined in claim 11 wherein reciprocation of the piezoceramic actuationassembly occurs at a frequency to couple a mechanical resonance of theshall and acoustic resonance of the piston, cavity and orifice forincreased amplification.
 15. The method as defined in claim 11 whereinreciprocating a piezoceramic actuation assembly connected between theend beams and intermediate the first and second pair of actuation beamson a non-interfering basis with the center shaft comprises inserting thecenter shaft through a collar interconnecting two piezoceramic stacks inthe piezoceramic actuation assembly.
 16. The method as defined in claim11 further comprising: interconnecting a second pair of laterally spacedflexing end beams with a third pair of opposing actuation beamsextending at an inverse angle from the pair of end beams and a fourthpair of opposing actuation beams extending at an inverse angle from thesecond pair of end beams, parallel to and longitudinally spaced from thethird pair of opposing actuation beams suspending the center shaft withthe piston from the third pair of opposing actuation beams and thefourth pair actuation beams; reciprocating a second piezoceramicactuation assembly connected between the second pair of end beans andintermediate the third and fourth pair of actuation beams on anon-interfering basis with the center shaft, said reciprocation out ofphase with the first piezoceramic actuation assembly.
 17. The method asdefined in claim 11 wherein the step of interconnecting a pair oflaterally spaced flexing end beams with a first pair of opposingactuation beams extending at an angle from the pair of end beams and asecond pair of opposing actuation beams extending at an angle from thepair of end beams, parallel to and longitudinally spaced from the firstpair of opposing actuation beams comprises providing a frame having ahexagonal structure incorporating the first pair and second pair ofactuation beams as rigid beams that are connected to opposing end beamsby a plurality of flexible joints and the step of suspending the centershaft comprises connecting the rigid beams to the center shaft by aplurality of flexible joints.
 18. The method as defined in claim 17further comprising machining flexible webs between the end beams andactuation beams and the center shaft and actuation beams as the flexiblejoints.
 19. The method as defined in claim 17 further comprising etchingflexible webs between the end beams and actuation beams and the centershaft and actuation beams as the flexible joints.